How to control power of a device from sysfs ?

[Ran Shalit]

On Mon, Dec 5, 2016 at 10:24 AM, Umair Khan <omerjerk at gmail.com> wrote:

> On Mon, Dec 5, 2016 at 12:56 PM, Ran Shalit <ranshalit at gmail.com> wrote:
> > Hello,
> >
> > I am trying to turn off screen using sysfs entries,
> > but I'm having some difficulties with it:
> >
> > 1.
> > command:
> > echo 0 > /sys/devices/platform/s5p-dsim.0/ea8061/backlight/panel/
> brightness
> > result:
> > screen is dimmed - BUT not turned off
> >
> > 2.
> > command:
> > cat
> > /sys/devices/platform/s5p-dsim.0/ea8061/backlight/panel/
> actual_brightness
> > 20
> >
> > This strengthen the fast that we didn't turned off brightness completely
> >
> > 3. In this point I though that maybe I can turn off the whole brightness
> > device
> >
> > ls /sys/devices/platform/s5p-dsim.0/ea8061/backlight/panel/
> > actual_brightness
> > auto_brightness
> > bl_power
> > brightness
> > device
> > dimming
> > max_brightness
> > power
> > subsystem
> > type
> > uevent
> >
> > I made some trials , but didn't made it turned off yet.
> > Is there any idea if it's possible to turn it off completely ?
>
> In my opinion, you'll need to have a look into the driver's code.
> See if that exposes a mechanism to turn off the screen at all.
>
>
Right,
Seems that sysfs exports features that drivers might not support (or
supported differently between different drivers)
for ea8061 driver:
Yet, not sure why on setting brightness 0 , I get that that it that
"catual_brightness" is 20.
See ea8061_set_brightness below.

https://github.com/gokhanmoral/siyahkernel-sgs3/blob/master-3.0.31/drivers/video/backlight/ea8061.c


static int ea8061_set_brightness(struct backlight_device *bd)
{
int ret = 0, brightness = bd->props.brightness;
struct ea8061 *lcd = bl_get_data(bd);

if (lcd->power == FB_BLANK_POWERDOWN) {
dev_err(lcd->dev,
"lcd off: brightness set failed.\n");
return -EINVAL;
}

if (brightness < MIN_BRIGHTNESS ||
brightness > bd->props.max_brightness) {
dev_err(lcd->dev, "lcd brightness should be %d to %d.\n",
MIN_BRIGHTNESS, MAX_BRIGHTNESS);
return -EINVAL;
}

ret = ea8061_gamma_ctrl(lcd, brightness);
if (ret) {
dev_err(&bd->dev, "lcd brightness setting failed.\n");
return -EIO;
}

return ret;
}

Thanks,
Ran


- Umair
>
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